Optical Sensing Pixel Circuit for Weak Fingerprint Signal Readout
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Solution Overview
Problem
The integration of fingerprint sensors on OLED display screens faces challenges due to weak currents output by photoelectric sensors, making it difficult to accurately obtain fingerprint information.
Innovation Solution
An optical sensing pixel circuit is introduced, comprising a photodiode to convert optical signals into electric signals, an amplification circuit to amplify these signals, and a constant current bias circuit to set a quiescent operating point, along with a current detecting circuit to convert large current signals into voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If photoelectric sensors are integrated on OLED display screens, then expenses are reduced and device volume/weight are decreased, but the weak currents output by photoelectric sensors (0.1 pA to 10 pA) make it difficult for fingerprint collection circuits to accurately read the signals
Solution Approach 1:
The patent introduces an amplification circuit as an intermediary component between the photodiode and the fingerprint collection circuit. This amplification circuit receives the weak current signal from the photodiode and amplifies it to a level that can be accurately read by the fingerprint collection circuit, thus resolving the measurement precision issue while maintaining the integration benefits
Solution Approach 2:
The patent employs a self-adjusting bias circuit that automatically adjusts the operating point of the amplification circuit based on the input signal level. This self-service mechanism ensures optimal amplification performance across varying signal conditions without requiring external manual adjustment, thereby maintaining high measurement precision
2Measurement precision
If amplification circuit is used to amplify weak electric signals, then detectable signal strength is improved, but circuit complexity increases
Solution Approach 1:
The patent combines the amplification circuit and the bias circuit into a single integrated unit that shares common components and control mechanisms. This merging approach reduces the overall circuit complexity while maintaining the signal amplification functionality, as the bias circuit's adjustment mechanism serves both the amplification and stability requirements
3Measurement precision
If constant current bias circuit is used to set quiescent operating point, then amplification accuracy is improved, but additional circuit components are required
Solution Approach 1:
The bias circuit is designed to serve multiple functions simultaneously: it sets the quiescent operating point for accurate amplification, provides signal stabilization, and enables automatic gain control. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall circuit complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively amplifies weak electric signals from photodiodes, enabling accurate detection and conversion of fingerprint information, thereby improving the functionality of fingerprint sensors on OLED displays.
Implementation Method 1
a photodiode, one end of the photodiode being electrically connected with a constant voltage end, wherein the photodiode is configured to detect an external optical signal and convert the optical signal into an electric signal
Data Source
AI summary
Disclosed are an optical sensing pixel circuit and a driving method therefor, and a sensor and a display panel. The optical sensing pixel circuit includes: a photodiode which is used for detecting an external optical signal and converting the optical signal into an electric signal; an amplification circuit which is electrically connected to the photodiode and used for amplifying the electric signal into a detectable large-current signal; and a constant current bias circuit which is electrically connected to an output end of the amplification circuit and used for providing a constant current for the amplification circuit so as to set a quiescent operating point having the same current as the constant current for the amplification circuit, such that the amplification circuit amplifies the electric signal on the basis of the quiescent operating point.